THE ROTATION OF CROPS 169 



Reduce Plant Diseases. — Plant diseases, like insect pests, are gen- 

 erally restricted to a particular crop or small group of closely related 

 crops. The potato scab, so far as is known, is confined solely to potatoes. 

 Its presence in the soil prevents the continuous growing of potatoes, and 

 calls for a rotation in which the interval between successive potato crops 

 is sufficiently long to provide for the disappearance of the disease. In a 

 similar manner flax wilt or cotton wilt demands a rotation of crops in 

 order to prevent the disease becoming disastrous. Bacterial diseases of 

 tomatoes, potatoes, eggplants, cabbage and numerous other "vegetables, 

 the rusts and smuts of small grains, and many other diseases accumulate 

 in the soil under the one-crop system. These troubles can be largely 

 avoided and the crop-producing power of the soil maintained by intelli- 

 gent systems of rotation. The most profitable system for any locality or 

 type of farming can generally be ascertained from the state experiment 

 station. 



Improve Environment of Crop. — Aside from insect pest, plant diseases 

 and weeds which flourish under the one-crop system to the disadvantage 

 of the crop, there is another factor inimical to best plant growth. This 

 consists of excreta given off by the roots of plants that accumulate in the 

 soil to their detriment. As a rule, such excreta are not equally injurious 

 to a different class of crops, and a rotation, therefore, lessens the injury. 

 The excreted substances are organic in nature and are either changed in 

 character or entirely disappear with time, so that the crop giving rise to 

 them may be returned to the land after a year or more without injury. 



Rotations Insure Returns. — The old adage, ''Don't place all your 

 eggs in one basket," applies with equal force in the production of crops. 

 Unfavorable conditions in any locality are seldom such as to cause a failure 

 of all kinds of crops, although a complete failure of a particular crop in 

 a certain locality is not uncommon. A rotation of crops which includes 

 a variety of crops, therefore, avoids complete failure. 



Prevent Reduced Crop Yields.— The tillage given to a cultivated 

 crop, such as corn or potatoes, increases the yield of the crop that follows 

 by providing a better physical condition of the soil. In like manner 

 legumes leave organic matter and nitrogen in the soil which is utilized to 

 the advantage of corn or potatoes which may follow. The cultivation 

 given crops destroys weeds to the advantage of crops which follow, and 

 which do not receive cultivation. 



Rotations Systematize Farming. — A well-planned rotation of crops 

 enables the farmer to know definitely what is to be done each year, and 

 makes possible an estimation of the general expenses and returns that 

 may be expected. It also enables him to plan his work and secure his 

 materials, such as seed, fertilizers, etc., in advance of the time they are 

 needed. 



Rotations Distribute Labor. — A good rotation of crops will enable 

 the farmer to do a larger proportion of his own work than would be possible 



